“The [RS-68] engine will be an upgraded version of those now used in the [Boeing] Delta IV, the largest of the Delta rocket family developed in the 1990s by the US Air Force,” says NASA.

The US space agency is investigating design options to improve injector performance in co-operation with the US military, while Pratt & Whitney Rocketdyne is the RS-68 prime contractor.

Because the RS-68 and Ares V upper stage’s Pratt & Whitney Rocketdyne J-2X engines share design features similar to the subscale hardware, data from the tests will also be used to develop the J-2X. It is also the upper stage engine for NASA's Ares I crew launch vehicle.